Telegraph repeater



Feb. l2, 1946. w. s. w. EDGAR, JR

TELEGRAPH REPEATER Filed Sept. 1'7. `1942 Patented Feb. 12, 1946 UNITED STATES PATENT OFFICEy TELEGRAPH REPEATER Application September 17, 1942, Serial No. 458,622

7 Claims.

This invention relates to telegraph systems and has particular reference to telegraph signal repeaters of the half duplex type arranged'to permit full duplex signaling over a main line circuit.

It is customary where a line circuit is operated on a full duplex basis to provide at the terminals of the circuit individual receiving and sending legs. Either or' both of these legs may b e extended by individual extension lines to a branch station. Independent signaling may be eiected simultaneously over the main line circuit and the receiving and' sending legs in accordance with well known principles. It sometimes becomes necessary to combine the legs in some manner because of a failure of one of the extension lines or of the apparatus associated therewith in order to provide temporary receiving and transmitting facilities to a branch station' connected to the sending and receiving legs. A combined sending and receiving leg is often made necessary as a permanent arrangement in cases where there is available only one extension line to a branch station. One arrangement of this character forms the subject matter of an application of V. R. Tolen, Serial No. 458,611, and entitled Telegraph repeater, led concurrently herewith. In the system disclosed in said copending application both sending and receiving signals may be transmitted over the combined leg, but such operations cannot of necessity be simultaneous. The eiect upon the main line circuit is that the signaling is on what is known as a half duplex basis.

When the terminal apparatus of a telegraphsystem is arranged to combine the sending and receiving legs. it sometimes is necessary to communicate with the remote terminal ofthe duplex main line circuit at a time when this terminal is transmitting. If the apparatusat the remote terminal is arranged in the conventional man--- ner for full duplex operation whereby individual sending and receiving legs areprovided the operation of a local transmitter at the station having the combined sending and transmitting leg would result in the transmission over the main line circuit and the reception by the remote statione receiving leg of. unintelligible signals.

Hence, it is one of the objects of the instant invention to provide an improved apparatus whereby the sending and receivingv legst of' a system normally operated on a full, duplex basis may be combined to enable the system to be. operated on a haii? duplex basis and whereby the main. line signaling at all times may be effected on. a full duplex basis.

Another object of' the invention is `to provide,

in a system having a combined sending and receiving leg, means whereby signals originating in the combined leg may be sent to a main line circuit as intelligible signals irrespective of the simultaneous application to the combined leg of signals received from the main line circuit.

A further object of the invention is to provide an electronic repeater associated with a local circuit havingtwo transmitters of like character and arranged in a novel manner to repeat signals from one transmitter but not the other.

Still another object of the invention is to provide an electronic repeater of the character described which is operable with both transmitters in concurrent operation.

An additional object of the invention is to provide a novel circuit arrangement to increase the gain in a direct coupled amplifier.

These and other objects of the invention are attained in the embodiment of the invention chosen for illustration and will become apparent from the following description which is taken in conjunction with the single figure of the accompanying drawing.

In the following description the values of resistances and voltages referred to are to be taken merely as illustrative and are not to bel construed in any way as limitations, since obviously other values may be selected b'y anyone skilled in the art to modify the arrangement to meet any speciiic conditions.

The main line circuit L, which at all times is operated on a full duplex basis, is terminated in the conventional duplex impedance bridge I. Signals received over the main line` circuit operate a receiver 2. Signals are transmitted to the main line by a transmitter 3. The receiver 2 is connected to control a local transmitting device A' by means of which the received line signals are repeated into a local receiving leg. Also, signals which are transmitted from a local sending leg operate a receiving device 5 by means of which the transmitter 3 is controlled to repeat the signals to the main line L.

The local sending and receiving legs may be extended by means of suitable extension lines t0 a branch station 6 at which are provided a combination transmitter-receiver T, normally used for sending, and acombination transmitter-receiver 8, normally used for receiving. The sending leg includes a series connection of a grounded negative battery 9, the receiving device 5, a jack IU, extension line Il, the combination transmitter-receiver l and resistance I2, and terminates in ground at the branch station 6. The

Y ground.

receiving leg includes the grounded negative battery 9, the transmitting device 4, ajack I3, extension line I4, the combination transmitter- Areceiver 8 and resistance I5, and also terminates in ground at the branch station 6.

VV2,394,538 Y a point in the first/described series'circuit between the transmitting element of the combina- ,k

. tion transmitter-receiving l and the transmitting V-Suchjan arrangement is customarily utilized for full duplex operation of a main line telef graph circuit, and independentsignaling may be eiected' simultaneously .over both the receiving and sending legs extending to the branch station 5.v In the event that a circuit failure of one of the extension lines occurs, either because of ka1 fault `in the line Wire itselfor because of the sending at Vthe time that received vmain lineY Yfailure of the printing equipmentlocated at the A signalsrare being relayed to the branch sta' tion. Of course, Vsince the transmitting and receiving elements of the branch station combination transmitter-receiver areV connected inY series, the received main line signals will not be properly recorded at the branch station. How-V ever, such a situation is not particularly serious,

Y since under theV circumstances, with the branch station operating withvtemporarily reduced facilities, about the only reason' for desiring4 to send lwould be to direct the station connected to the re-l mote terminal of the main line circuit to repeat something which hadupreviousl-y beeny sent but which may not have been properly received. In

a repeat of the communication erroneously receivedbut also that portion of the communicatinWhich he himself mutilates'by the operation of histransmitting apparatus.

- The repeating arrangement in accordance with the invention permitsthe transmission vof the signals sent from a branch station during the time that -*signals are also beingreceived thereat so that'th'estation connected to the remote terminal of the mainline circuit is furnished with V'an Vintelligible communication. v

Assume 'that the normal receiving leg includ` ing the'eXtension line I4 and the combination transmitter-receiver 8 is temporarily incapacitate'd. Repeating apparatus whichl terminatesl in a pair of double conductor plugs I5 and Vi is connected to the sending and receivingr legs by the insertion ofthe respective plugs in jacks I0 and I3. A switch blade I8 is placed in engagement with its upper contact, as shown, and the apparatus is conditioned to function by using the extension line I I and the combination trans mitter-receiver 1 in'a combined sending and ren ceiving leg. In this case a series circuit is formed and includes grounded Vnegative lbattery 9, the transmitting device 4, the respective sleeve elements of jack I3 and plug Il, a monitor jack I 9, switch blade I8 and its upper contact, the respective tip elements of plug I 5 and jackV I0, extension line II, combination transmitter-re- Yceiver 'l and resistance I2 and terminates in ground. Another series circuit is formed and includesthe grounded negativebattery 9, the re- Y ceiving device 5, the respective sleeve elements of jack I0 and plug I6 and the space discharge path of a vacuum tube 20 and terminates in Connected to the switch blade I8, which is at 'such a case the branch station will obtain notonly device 4, is a circuit including resistances 2| and 22V extending to kthe control grid ofV another vacuum tube 23. The cathode of this vacuum' tube is connected to abottom voltage divider lcomf prising the series connection of'resistances 24, Y25, Y'

2t and 2l. The terminals ofY this voltage divider .are connected across the terminals of batteries 9 and 28.V These batteries are arranged to aid one another, and the positiveV terminal of the combination is connected to ground. Ithas been found rin practice/that,V When'the total voltage ofthe batteries 9 and .28 is Yapproximately 250 volts, satisfactoryresults may'be obtained when the approximate values of the bottom voltage dividerV resistances 24, 275, 26 and 21 are 7,500, 2,500, 5,000 Vand 10,000 ohms respectively.V Another connection is made to the kcontrol grid circuit of tube 23 through a current limiting resistance 29 toa point on the bottom voltage divider for a purpose to be described. The value of the ree sistance 29 should be high enough to prevent the. short-circuiting of thetransmitting' device 4.

The amplifier repeater is also vprovided 'with a top voltage divider comprising the series Ycon-Y nection of resistances 30, 3| and 32. vThe ter-l minals of this Voltage divider are alsoconnected across the terminals of batteries 9 and 28. For the voltage previously specified,V the approxie mate values of the top voltage divider resistances 3l), 3I and 32 should be 0.15, `0.6 'and 0.6 megohms, respectively. Theranode of tube 23 is con-V nected to the top voltage dividerin Va manner to influence the rcontrol grid of another vacuum tube 34, said grid also beingconnected to this voltage divider. The cathode of the tube 3d is connected to a point on the bottom voltage divider,

and the Yanode Vis connected through a relatively high resistance 35'to the grounded positive ter minal of battery 9. VThe control grid of tubeEIl is Y also connected to the anode of tube 34 and, consequently, is'inluenced by the operation of the latter tube. Space current for the tube 20 is` derived from theY grounded vpositive terminal lof battery 9 through a resistance 36and also iloWs through theV receiving device 5 toV which lthe Ving at the branch station transmitter.

cathode of the 'tube is connected. Y

Where a receivingdevice corresponding to the receiver 5 is of a character requiring only a`Y relatively small amount of energy for its operation,

the electronic repeater may comprise only ythe Y equivalent of tube 23. However, when it is necessary tor amplify the signals originating'at the branch station transmitter, the tubes Zlan'd 34 Will be necessary. Two additional tubes are,Y needed, since. it is inherent in any low frequency ,directz coupled amplifier' that ythe signals ap. pearing in the output circuits of successive tubes are out of phase by In the Vpresent instance, the signals appearing` in` the output circuit of. the tube 23 are in phase with the signals originate Consequently, the signals inthe output circuit of the tube 34 are 180? out ofphase with the signals extension lineV II as assumed, let it furtherbe assumed that the transmittingfelement of thev combination transmitter-receiver 'I and the transmitti-ng device 4 are in their marking orl circuitclosin-g positions. Where the voltage oi the grounded negative battery Sis approximately'halff of' the Ycombined voltages of the batteries 9 and 28 or, inother words, 125 volts, the impedances in the series circuit including the tvvoI transmitting devices arechosen so that the vpotentialv at the switch blade I3 is approxi-mately nega-tive 60 volts. This potential is applied through resistances 2l and 22 to the control grid of the tube 23 and, since the cathode of this tube is connected to a point 31 on the bottom voltage divider, at which the potential is approximately negative 85 volts, the tube is conditioned for the conduction of space current. This current flows from thev grounded positive terminal lof the batteryv S, through resistance 30 of the top voltage divider. the tube 23, and resistances 25, 26, 2."` of the bottom voltage divider to the negative terminal of the battery 28. 'Ihe voltage drop through the resistance 30 results in the application to the control grid of the tube 34 of a potential Vof approximatelyr negative 175 volts derived from a point 38 on the top voltage divider. Similarly, the voltage vdrop through resistances 25, 215 and 2*? causes the application to the cathode of the tube 34 of a voltage of approximately negative 16'5 volts derived from a point 39 on the bottom voltage divider. Consequently, since the grid ofl the tube 34 is at a negative potential with respect to its cathode, this tube is not conditioned for Aconduction. With no space current 'being conducted in the tube 34, there vis no voltage drop across the resistance 35, and consequently the control grid of tube 20 is at ground potential. The cathode of this tube, however, is at a negative potential derived from the battery 9 through the receiving device 5. Therefore, the tube is conditioned for the conduction of space current,' and a marking condition is applied to the receiving device 5.

If, while the combination transmitter-receiver 'i of the branch station 6 is inoperative, that is, with its transmitting contacts in the closed or marking position, the transmitting device 4 operates by opening the local series circuit for the relaying of a spacing signal derived from the receiver 2 in response to the reception of a spacing signal from the line L, the connection to thel negative terminal of the battery 9 is broken. Consequently, the potential of the switch blade i8 and also of the control grid of the tube 23 is zero or ground derived from the branch station S. Thus, it is seen that the grid of the tube 23 is even more positive with respect to its cathode tha-n before, with the result that the tube con tinues` to conduct. Since this tube controls the operation of the other two and the receivingv device 5, there is no response by the latter to the spacing signal repeated from the main line circuit L to the branch station 6.

When the transmitting device 4 is inoperative, that is, in the closed or marking position, and the transmitting element of the combination tran-smitter-receiver 'I opens to send a. spacing signal from the branch station 5, ground is disconnected from the series circuit to interrupt the flovvr of current therein, thereby leaving the switch blade i8 and the control grid of the tube 23 at a negative potential approaching that of the battery 9 which, as assumed, is approximately 125 volts.

The grid of the tube 23 then is suiciently negative with respect to its cathode to render the tube non-conducting. The voltage drop across the top voltage divider resistance 30 decreases, with the result that point 40 becomes' less negative.

As a consequence, the point 38. also/becomes: liess negative and has a value of approximately negative 1555 volts. This potential, being applied to ythe grid of the tube 34, tends to condition the tube to become conducting. At the same time the interruption of the space currentvof the tubeiz results in a decrease in the voltage drop across resistances 25, 26 and 21 of 'the bottom voltage divider, with the result that points 31 and 3% Abei- 'comemore negative, vthe 'latter having :a value of approximately negative volts. potential being applied to the cathode of 'the tube 134, also tends to cause the conduction of space current in this tube; This arrangement forms an impor` tant feature or the amplifier, since not only is the control grid ofthe tube 34 influenced by the tube 23 but also the cathode of tube V34 is influenced thereby andvin an opposite sense. Consequently, the gain obtained in the amplifier stage including the tube 3'4 is materially greater than Athat obtainable Where only the control grid po tentials are varied in accordance with the operations of' the tube 23.

With the conduction of space current through the tube 34, the voltage drop across the 'resistance '35 results in the application to the control grid of the tube 20 of a potential which is suinciently negative with respect to its cathode to interrupt the" space current in the tube and also 'through the receiving device 5. Thus, the spacing :signal v'originating `at the branch station transmitter is repeated to the receiving device 5 by means of which 'the transmitter 3 'is controlled to 'further repeat the 'spacing signal to the main line circuit L.

The operation of lthe system described up to this Apoint is in general accordance with well known half-duplex 'principles of operation. If, white the transmitting device 4 'is operating to repeat signals received from the main line circuit L to the branch station combination transmitter-receiver '1, the `operator at the vbranch station operates the transmitting element of the combination transmitter-receiver, the receiving element of this device Will not record the signals sent by the transmitting device4 in a proper manner, since these signals will be mutilated.

Of the four signa-ling combinations possible with both the transmitting device. 4 and the transmitting element ofthe combination transmitter-receiver l in simultaneous operation, three have been described; The fourth one of these combinations is when both transmitters are in their open circuit positions for the transmission of spacing signals. In this case, ground is disconnected from one end of the combined sending and receiving leg by the transmitting element of the combination transmitter-receiver 1, and negative battery 9 is disconnected from the other end of the combined leg by the operation o1 the transmitting device 4. The connection of the grid of the tube 23 through resistance v29 to a. point 4l on the bottom voltage divider conditions the tube for non-conduction, vsincev the point 4I is suiiiciently more negative than the point 31, to which the cathode of the tube is connected, to bias the tube to cut off. (Ilonseoluently,y the ampliner repeaterv functions to repeat the spacing signal sent from the branch station to the main line circuit.

1f it is desired to use the extension lineA I4' `as part of the combined sending and receiving leg, the switch blade Iis placed; in engagement with its lower contact. The series circuit including the transmitting vdevice 4 then includes the combination transmitter-receiver 8 Yof the branch' station 6. The operation4 of. the amplifier rey Ypeater is the same as that previously described.

'A condenser 42 is connected from `a point in the i circuit oi?Y the control grid of tube 23 to ground for the purpose of `preventing the impression upon this grid Yof transient voltages caused by the operation of either transmitter and having values'in excess of the steady `Vstatefvoltages which appear in the combined sending and receiving leg. The transient voltages result from the opening and closing by the transmitters of thecircuit including theinductancecf the receiving element of the combination transmitterreceiver. Suchr voltages, if allowed to influence the grid'rof thetube23, would cause false operations of the repeater. v

When the system is arranged for normal full duplex operation with individual sending and receiving legs, a monitor printer 43 comprising transmitting and receiving elements may be connected in either the sendingor receiving leg by the insertion of a plug 44 into jjacks HJorv I3, respectively. f Y

The sending and receiving. legs are normally Y connected through contacts `of jacks I and I3, respectively, and include the'respective resist-V ances 45 and 45. Such resistances are proportioned to balance the resistance of either the monitor printer d3 or the amplifier repeater, de-

' pending upon which is plugged into the jacks,

so that at all times the current owing in the Vsending Vand receiving legs is Vsubstantially the same. The monitor jack i9, into which the plug 46 is inserted for monitoring purposes when the apparatus is arranged to combine the sending and receiving legs, is also provided with a similarV resistance 41. for substantially the Ysame purpose. The nature of the invention may be ascertained from the foregoing description of an'illustrative. Yembodiment thereof, it being understood that other modifications embodyingthe sameV inventive idea may be made 4Within the'scope of vvvhat .is claimed without departing from the spirit of the invention. V

What is claimed ist.

l. nIn a telegraph system, a dupleXed main line circuita local .circuit associated with one termi-V nal of said main line circuit includingY trans mitting andreceiving legs, sending and receiving apparatus in each of lsaid legs, a repeater between said mainline circuit and said transmitting and receivinglegs, means associated withv said repeater for preventing the reflection into said mainline circuit of Ysignals received there,- frorn, and means to condition one of said legs for .transmission of intelligible signals from the sending apparatus therein to said duplexed line circuit concurrently with the application of signals to, saidlegfrom said duplexed line circuit and for the repetition of intelligible signals from said dup-exedline circuit over said leg, to the receiving apparatus therein during idle periods of transmission over said vleg to said dupleXed line` circuit. Y

v receiving leg.y

vmeans. forrepeating toisaid main line circuit intelligible signals transmitted over said combined sending and receiving lleg both during vbusy and idle periods of application of signals from said mainline circuit tolsaid combined sending and 3. In a telegraph system, a duplexed main line circuit, a first series local circuit including a main- Y line signal receiver, a local transmitter'and local receiver, said local receiver being responsive both to said main line signal receiver'and to Vsaid local transmitter, a second local circuit including a;

mainline signal transmitten'an electronic repeater having an input circuit connected to said rst local circuit for repeating to said local re. 'ceiver signals received over said duplexed main line circuit and an output circuit connected to,Y .Y

said second local circuit for repeating to said dupleXed main line circuit -signals originating at n said local transmitter, and means for biasing said repeater to relay to said main line signal transmitter only the signals originating at said local transmitter'irrespective of the concurrent'operation of said main line signal receiver. Y 4. In a telegraph system, aV dupleXed main line circuit, a first local circuit including'a mainline signal repeating device, a transmitter and a receiver, said receiver being responsive both to said repeating. device and' to Vsaid transmitter, a sec ond local circuit including a main lineV signal transmitting device, an electronic repeater hav-r Ying an input circuit connected to said firstilocal circuit for repeating to saidrlocal receiver signals received overV said duplexed main line circuit and an output circuit connected to saidsec- Y ond local circuit for repeating to said duplexed main line circuit signals originating at said local transmitter, means utilizing potentials of a point in said first localcircuit to render said repeater operative in response to'operations of said transmitter and inoperative in response to'op'erations `of saidfrepeating device whereby only'said trans- Y Vmitter signals actuatersaid transmitting device,

2..In a telegraph system, a main line circuit, Y

a local circuitincluding combined sending and cuit signals originating in said sending leg facilities and to prevent the'relaying to said main line circuit ofslgnals destined for said receiving leg facilities, and-means for utilizing one of said legs for combined sending and receiving, including and'means for biasing said repeater to repeat saidk transmitter signals to said transmitting device irrespective of ythe concurrentoperation of said repeating device. r Y

' Y 5. In a telegraph system, a series circuit including tWo impulse transmitters and having one terminalconnected to a .grounded source of direct currentY and the other terminal connected Yto ground, a signal translating device, an electronic repeater having its output circuit connected to control said translating device, means for con-V necting the input vcircuit ofv said repeater from ground, to a point on said series circuit between said transmitters whereby the signals Vof both of .said transmitters modify the input potential to Y.

said electronic repeater, and means for biasing the input'circuit of said repeater to repeat'tlfieY signals of one of said transmitters only irrespective of the concurrent operation of both of said transmitters.' 'f

6. In a'telegraph system, a duplexed mainline circuit, a rst local circuit including a main line signal receiver, a local transmitter. and a local receiver, said local receiver being responsive both to said main line signal receiver and to said local transmitter, a secondl local circuit including a main line signal transmitter, an electronic Vrepeater, means utilizing potentials derived from said first local circuit to control the operation of said repeater to relay to said main line signal transmitter .signals from said local transmitter and tol prevent the relaying to said main line sig- 'Y nal transmitter of signals from said main line signal receiver, and means utilizing an auxiliary potential to condition said repeater for said operation irrespective of the concurrent operations of said main line signal receiver and said local transmitter.

7. In a telegraph system, a duplexed main line circuit, a local circuit including a series connection of a grounded source of negative potential, a main line signal repeating receiver, a local receiver and a local transmitter connected to ground, said local receiver being responsive to operation of said main line signal repeating receiver and to operation of said local transmitter, a main line 

